The present invention relates to industrial control systems and, in particular, to power and communications cabling for use with a motor and a drive unit in an industrial control system.
Industrial controllers are specialized computer systems used for the control of industrial processes or machinery, for example, in a factory environment. Industrial controllers typically control numerous modules via specialized control networks for accomplishing different tasks in the industrial system. One such module may be a variable frequency drive (“VFD”) unit, which, in turn, may deliver power to, communicate with and control a motor. In industrial applications, motors may be used to affect a variety of motions in the industrial process. For example, motors may be operated at continuous or variable speeds, such as for turning the blades of a fan or the rollers of an assembly line at constant or variable speeds at different times, or may be used to precisely control the position of objects and machines, such as precisely controlling the movement of a robotic arm or the opening and closing of a door.
Drive units typically have access to a power source and utilize a transistor network to deliver high voltage three phase electric power to a motor. Motors typically receive power from the drive unit and in turn feed the power through electrical windings which surround a motor core with one or more magnets, thereby electromagnetically powering the motor. Delivery of such power to the motor typically requires transmission of significant amounts of power and energy, which is inherently a source of electrical interference and noise. As such, drive units typically deliver such power via dedicated power cables to minimize electromagnetic interference (“EMI”).
Drive units also typically provide data communication and control over the motor. Such data communication may be bi-directional between the drive unit and the motor. For example, drive units may send communications to the motor to turn the motor on, adjust the position, adjust the direction, adjust the speed, or apply a brake, such as during an emergency. Drive units may also receive communications from the motor, such as for measuring the precise position of the motor, speed (revolutions per minute), temperature, or run-time.
Motors typically include encoders which may precisely measure (or sense) the position of the motor or which may communicate with one or more other intelligent sensors or devices integrated with the motor, such as a temperature sensor or timer. The encoders may communicate such information to the drive unit. Encoders may communicate information via one or more digital data signals over a transmission line, which may be for example a single-ended line or a differential pair.
All such communication transmission lines typically involve low voltage electrical signals that are susceptible to electrical interference and noise, which may thereby cause signal integrity loss and resulting data loss. Consequently, drive units typically communicate with motors via dedicated communications cables.
Current implementations requiring multiple cables for separate power delivery and communications thereby increasing the cost and complexity of the designs by automatically doubling the number of cables and connectors that are required. On the other hand, recent attempts toward combining power and communication conductors in a single cable continue to suffer from electrical noise and interference drawbacks on the data communication lines as described above, thereby limiting their possible range of transmission line lengths, data communication speeds and system reliability.